1. Field of the Invention
The invention relates to a frequency synthesizer, and in particular to a frequency synthesizer in a Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wideband (UWB) system.
2. Description of the Related Art
Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wideband (UWB) systems (referred to as MB-OFDM UWB systems hereinafter) include a working spectrum from 3.1 GHz to 10.6 GHz, the spectrum is divided into 14 bands, each comprising 528 MHz. FIG. 1 is a spectrum diagram for a MB-OFDM UWB system, comprising first frequency band b1 to fourteenth frequency band b14, each frequency band comprises a carrier frequency, referred to as first frequency f1 to fourteenth frequency f14 and located at 3432 MHz, 3960 MHz, 4488 MHz, 5016 MHz, 5544 MHz, 6072 MHz, 7128 MHz, 7656 MHz, 8184 MHz, 8712 MHz, 9240 MHz, 9768 MHz, and 10296 MHz respectively. Every three frequency bands are grouped to provide first group BG1 to fifth group BG5. Note fifth group BG5 only comprises frequency bands b13 and b14.
Based on MB-OFDM UWB standard, a frequency synthesizer in a MB-OFDM UWB system must provide the three frequency bands in first group BG1 from 3.1 GHz to 4.8 GHz, referred to as Mode-1 (or Mandatory) operation. The MB-OFDM UWB system can optionally provide frequency bands exceeding 5 GHz to provide high data throughput, referred to as Mode-2 operation. Since fast switching between the frequency bands (≦9.5 ns) is required in the operation, the conventional phase lock loop (PLL) cannot meet system requirements. Utilizing frequency mixing technique to generate the required frequencies selected by the multiplexers provides a feasible solution. However, related disclosures [1] to [7] are only applicable to Mode-1 operation. Disclosure [8] supports Mode-2 operation, but only generates 7 frequency bands, rather than the fourteen frequency bands for the MB-OFDM UWB system. Disclosure [9] supports all fourteen frequency bands, but comprises a PLL and 5 mixers, and possibly generating large noise and degrading transmission signals.
Current telecommunication development aims for high speed/high volume wireless communication. A MB-OFDM UWB device can offer the solution to such requirements of additional functions beyond telecommunication. Thus a need exists for a frequency synthesizer covering the whole spectrum for a MB-OFDM UWB system, comprising minimum numbers of single sideband mixers to reduce the generated spurs.
[1]: IEEE 802.15.3a, Updated MB-OFDM Proposal Specification (03/268r3), March 2004, by MBOA
[2]: C. F. Liang and S. I. Liu, “A Fast-Switching Frequency Synthesizer for UWB applications,” IEEE 2005 Asia Solid-State Circuit Conference, 8-2, November 2005, pp. 197-200
[3]: C. C. Lin and C. K. Wang, “Subharmonic Direct Frequency for Mode-1 MB-OFDM UWB System”, IEEE 2005 Symposium on VLSI Circuits, 3-3, pp 38-41.
[4]: C. Sandner, et al., “A 3 GHz to 7 GHz Fast-Hopping Frequency Synthesizer for UWB,” International Workshop on Ultra Wideband System, 2004, 18-21, May 2004, pp. 405-409.
[5]: D. Leenaerts, et al., “A SiGe BiCMOS ins Fast Hopping Frequency Synthesizer for UWB Radio,” 2005 IEEE Int. Solid-State Circuit Conference, 11-2, pp. 202-203.
[6]: Hyun-Su Chae, et al., “A Fast Hopping Frequency Synthesizer for UWB Systems in a CMOS Technology,” Int. Symp. on Wireless Communication Systems 2005, 5-9 Sep. 2005, pp 370-374.
[7]: Remco van de Beek, et al. “A fast-hopping single-PLL 3-band UWB synthesizer in 0.25 um SiGe BiCMOS,” Proceedings of 31th ESSCIRC 2005, 12-16 Sep. 2005, pp. 173-176.
[8]: Jri Lee and Da-Wei Chiu, “A 7-band 3-8 GHz Frequency Synthesizer With 1 ns Band-Switching Time in 0.18 um CMOS Technology”, IEEE 2005 Int. Solid-State Circuit Conference, 11-3, pp. 204-205, 2005.
[9]: C. Mishra, et al., “Frequency Planning and Synthesizer Architectures for Multiband OFEM UWB radios,” IEEE Trans. on Microwave Theory and Techniques, vol. 53, issue 12, December 2005, pp. 3744-3756.